The present invention relates generally to cable ties and relates more particularly to a method of making cable ties using an insert molding technique and also to cable ties made by said method.
Cable ties, also known as bundling ties and harnessing devices, are well known devices commonly used in the art to couple together a plurality of elongated objects, such as wires or cables. One type of cable tie which is well known and widely used in the art comprises an elongated strap having an apertured head disposed at one end thereof. The opposite end of the elongated strap is typically shaped to define a tail of narrowed width adapted for insertion through the apertured head to form a closed loop. A plurality of serrations or teeth are formed along the length of the elongated strap, and an internal pawl (or locking tang) is disposed within the apertured head, said internal pawl being adapted to prevent a serration on the strap, once inserted past said internal pawl, from being withdrawn therepast. In this manner, the engagement of the internal pawl with the serrated strap is used to lock the cable tie in a closed loop configuration.
Examples of cable ties of the above construction are disclosed in the following U.S. patents, all of which are incorporated herein by reference: U.S. Pat. No. 4,658,478, inventor Paradis, issued Apr. 21, 1987; U.S. Pat. No. 4,754,529, inventor Paradis, issued Jul. 5, 1988; U.S. Pat. No. 5,593,630, inventors Sorensen et al., issued Jan. 14, 1997; and U.S. Pat. No. 5,669,111, inventor Rohaly, issued Sep. 23, 1997.
Another type of cable tie which is well known and widely used in the art differs from the above-described cable tie in that it comprises an apertured or ladder-type strap, instead of a serrated strap. The head of the cable tie typically has a buckle-like shape and includes a tongue that is adapted to enter the apertures of the strap to lock the strap in a fixed loop configuration.
Examples of cable ties of the above ladder-type strap construction are disclosed in the following U.S. patents, all of which are incorporated herein by reference: U.S. Pat. No. 3,766,608, inventor Fay, issued Oct. 23, 1973; U.S. Pat. No. 4,347,648, inventor Dekkers, issued Sep. 7, 1982; and U.S. Pat. No. 4,866,816, inventor Caveney, issued Sep. 19, 1989.
Cable ties, whether of the serrated-strap variety described above or the ladder-strap variety described above, are typically formed by injection molding. More specifically, this typically involves the use of a two-piece mold into which the impression of one or more whole cable ties has been formed. Molten plastic (more typically nylon and less typically polypropylene) is injected into the mold through a single opening or gate in the mold until the one or more impressions therein are filled. The molten plastic is then allowed to harden in the one or more impressions. The thus-formed cable ties are then removed from the mold.
The present inventor has noted the following disadvantages associated with the aforementioned injection molding technique for making cable ties: First, because the above-described process involves molding the entirety of a cable tie at one time, the length of the cable tie strap is necessarily limited by the size of its corresponding impression. Consequently, to make a variety of cable ties having straps of different lengths, it is generally necessary to use different sized impressions. This typically results in the need for many differently-sized molds as the impressions of any given mold are typically fixed in size and identical to one another. As can readily be appreciated, the provision of many differently-sized molds may be prohibited by cost as molds are very expensive to produce. Moreover, the use of different sized molds may require the adaptation of other equipment used in the manufacturing process.
Second, because the above-described process requires that the entirety of the cable tie be formed at one time, cable ties having long strap lengths (i.e., several feet) require correspondingly large molds. Molds of such large size are particularly expensive to produce. In addition, because cable tie molds typically have only a single gate through which molten plastic is injected (to prevent the occurrence of knit lines—especially in those instances in which nylon is the molten plastic used), the cycle time can be rather long as the molten plastic must travel through the single gate in the mold until it fills the entireties of all of the impressions. In addition, the aforementioned forcing of the molten plastic through the entireties of the impressions often results in some degradation of the molten plastic material, such degradation being undesirable.
One patent of interest is U.S. Pat. No. 6,003,209, inventors Oh et al., which issued Dec. 21, 1999, and which is incorporated herein by reference. In the aforementioned patent, there is disclosed a filamentary fastener and a method of making the same, the method comprising the steps of (a) providing a length of flexible filamentary material; (b) providing a mold, said mold being shaped to include a paddle impression and a cross-bar impression, said paddle impression and said cross-bar impression being parallel to one another; (c) insert molding, using said mold, a first paddle and a first cross-bar onto said length of flexible filamentary material; (d) repositioning said length of flexible filamentary material relative to said mold so that said first paddle and said first cross-bar are spaced apart from said mold; (e) insert molding, using said mold, a second paddle and a second cross-bar onto said length of flexible filamentary material; and (f) cutting said length of flexible filamentary material between the paddle and the cross-bar formed during the same molding iteration to yield a fastener having a flexible filament with a paddle at one end and a cross-bar at the opposite end.
The process of the aforementioned patent is not adapted to making cable ties, but rather, is limited to making filamentary fasteners of the type having a cross-bar at one end thereof. In addition, the present inventor has noted that, with respect to the process of the aforementioned patent, the cutting step is performed after the second insert molding step. This is disadvantageous to large-scale production because only one fastener at a time can be formed using a given filament.
Another patent of interest is U.S. Pat. No. 4,636,347, inventor Kato, which issued Jan. 13, 1987, and which is incorporated herein by reference. The aforementioned patent relates to a fastener comprising a female member having an opening, a male member which is engageable in the opening of the female member and a string member joining the female and male members. The patent also relates to a fastener assembly comprising a plurality of such fasteners joined together. The female and male members of the fastener are molded from a thermoplastic synthetic resin and are fused to the string member. The fastener or fastener assembly is made by a method comprising placing a string through a female member forming mold and a male member forming mold, supplying a molten thermoplastic resin into the molds to form a female member and a male member, removing the molded female and male members from the molds, moving the string forward, repeating the molding of a plurality of female and male members, and if appropriate, cutting the string between the female member of one fastener and the male member of another.
The process of the foregoing patent is beset with the same types of limitations discussed above in connection with the process of U.S. Pat. No. 6,003,209 (i.e., said process is not adapted to making cable ties and requires the second molding on a string before the string can be cut).